ClickHouse/dbms/src/Interpreters/evaluateMissingDefaults.cpp
2018-09-20 14:16:15 +03:00

68 lines
2.2 KiB
C++

#include <Core/Block.h>
#include <Storages/ColumnDefault.h>
#include <Interpreters/ExpressionAnalyzer.h>
#include <Interpreters/ExpressionActions.h>
#include <Interpreters/evaluateMissingDefaults.h>
#include <Parsers/ASTExpressionList.h>
#include <Parsers/ASTWithAlias.h>
#include <utility>
namespace DB
{
void evaluateMissingDefaults(Block & block,
const NamesAndTypesList & required_columns,
const ColumnDefaults & column_defaults,
const Context & context)
{
if (column_defaults.empty())
return;
ASTPtr default_expr_list = std::make_shared<ASTExpressionList>();
for (const auto & column : required_columns)
{
if (block.has(column.name))
continue;
const auto it = column_defaults.find(column.name);
/// expressions must be cloned to prevent modification by the ExpressionAnalyzer
if (it != column_defaults.end())
default_expr_list->children.emplace_back(
setAlias(it->second.expression->clone(), it->first));
}
/// nothing to evaluate
if (default_expr_list->children.empty())
return;
/** ExpressionAnalyzer eliminates "unused" columns, in order to ensure their safety
* we are going to operate on a copy instead of the original block */
Block copy_block{block};
/// evaluate default values for defaulted columns
NamesAndTypesList available_columns;
for (size_t i = 0, size = block.columns(); i < size; ++i)
available_columns.emplace_back(block.getByPosition(i).name, block.getByPosition(i).type);
ExpressionAnalyzer{default_expr_list, context, {}, available_columns}.getActions(true)->execute(copy_block);
/// move evaluated columns to the original block, materializing them at the same time
size_t pos = 0;
for (auto col = required_columns.begin(); col != required_columns.end(); ++col, ++pos)
{
if (copy_block.has(col->name))
{
auto evaluated_col = copy_block.getByName(col->name);
if (ColumnPtr converted = evaluated_col.column->convertToFullColumnIfConst())
evaluated_col.column = converted;
block.insert(pos, std::move(evaluated_col));
}
}
}
}